However, it is quite clear that if a stream of air sets ice in motion, the moving ice, in turn, 

 will exert an influence on the layers of air above it. 



In this respect, the observations of Efremov are very interesting. They were made in July 

 1939, during the drift of the Sedov in the Arctic Basin, in the region between 85°23' and 

 85°50'30" north and 58°27' and 64°21' east (table 97). 



TABLE 97. WIND SPEEDS AT VARIOUS HEIGHTS ABOVE THE SURFACE OF ICE 

 (IN PER CENT OF THE WIND SPEED ON THE BRIDGE OF THE SHIP) 



From the table it is evident that the wind speed at the surface of the ice on an average was 

 24 per cent of the wind speed measured on the bridge of the Sedov 12. 5 m above the surface of the 

 ice. 



During the drift of the station "North Pole" ("Severnyi Polius"), the wind speed was meas- 

 ured at a height of 2m. From the table it is evident that on an average one may consider that the 

 wind speed was about 66 per cent of the wind speed at the height of the Sedov bridge. 



Theoretical concepts indicate that the wind direction should also differ at different heights 

 above the surface of the ice, but to my knowledge no supporting investigations have been made as 

 yet. 



The problem of the magnitude and direction of the hydrodjmamic resistance offered by the 

 water to the ice under various circumstances is equally complex and as far as the theoretical con- 

 cepts go we must rely on fairly well-founded assumptions. 



LITERATURE: 62, 72, 77. 



Section 133. The Drift of Close Ice Fields 



The first systematic investigations of the drift of close ice fields were made by Nansen during 

 the expedition on the Fram in 1893 to 96. These investigations were particularly important in that 

 the drift of the Fran passed over a deep part of the ocean, far from the distorting influence of the 

 coastline . 



356 



